Cathode for an electric discharge tube



April 1965 H. G. GERLACH ETAL 3,177,393

CATHODE FOR AN ELECTRIC DISCHARGE TUBE Filed Aug. 21. 1961 5 H :9) gm 2 F l z 9 7 z 5 2 z 2 s 1 Fa g ei 10 3% g s a Ea f" e 4 I 7 u I FIG. FIG.2 F163. FIG! INVENTORS HANS G.GERLAGH WILHELMUS AJURGENS BY W K Q-+ United. States at 3,177,393 CATHODE FOR AN ELECTREC DISCGE TUBE Hans Georg Gerlach and Wilhelinus Albert Jurgens, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 21, 1961, Ser. No. 132,835 Claims priority, application Netherlands, Oct. 14, 196%, 256,883 6 Claims. ((11. 313-278) Our invention relates to a cathode for an electric discharge tube, and in particular to a directly heated cathode for a transmitting tube, in which the cathode consists of a plurality of thin wires connected in parallel.

In certain cases it is desirable that an electric discharge tube be ready for operation substantially immediately after potentials are applied thereto. For example, in mobile or portable transceivers, the transmitting tubes are switched off while receiving in order to reduce the filament current consumption, and switched on to transmit so that a quick heating cathode is desired.

While directly heated cathodes which consist of a number of thin filaments connected in parallel are known in which the operating temperature is reached very rapidly after potentials are applied, in order to obtain a sufficiently large emitting surface, a large number of thin wires have to be connected in parallel which presents difiiculties in the suspension and the mounting of the cathode in the tube.

If the wires are connected to two parallel cross bars, these bars, during the construction of the system, must be connected to supporting members and tensioning springs. Since the thin wires have no stitfness and the cathode does not form a unit which can readily be handled, the mounting of the cathode in the electrode system is not simple.

It is an object of our invention to provide a quicklyheating directly heated cathode for an electron discharge tube in which mounting and suspension problems are simplified.

Another object of our invention is to provide a cathode comprising a plurality of thin Wires which can be easily supported and mounted in an electric discharge tube.

These and further objects of our invention will appear as the specification progresses.

The cathode, in accordance with our invention comprises a plurality of fine wires wound on two U-shaped caps which are insulated from one another, which caps are slidable on two oppositely located ends of a supporting plate. The supporting plate with the caps and the cathode wire form a unit which can be easily handled. The covered cathode wire may then be wound on these caps in a simple manner, in which the emitting material of the parts which come into contact with the caps is removed by means of a scraper during winding, at least on that side of the wire which isto engage the U-shaped caps. Supporting rods are provided on these caps for the mounting of the cathode unit in the electrode system.

If the supporting plate consists of metal, the ends, on which the U-shaped caps have to slide, have to be covered with an insulating layer; but this is not necessary if the supporting plate consists of insulating material.

After the cathode is mounted in the electrode system, spring action is made to act upon the U-shaped caps in opposite directions, as a'result of which the wires are kept strained because the caps are slidable on the supporting 7 plate.

In order that the invention may readily be carried into efiect, three embodiments thereof will now be described,

by way of example, with reference to the accompanying drawing, in which:

FIG. 1 is a longitudinal sectional view of a cathode unit according to the invention;

FIG. 2 is a side view of the embodiment shown in FIG. 1; 7

FIGS. 3 and 4 are a longitudinal sectional view and a side view respectively of another embodiment; and

FIG. 5 is a longitudinal sectional view of still another embodiment according to the invention.

In FIGS. 1 and 2, the emitting cathode wires 1 which may consist, for example, of a tungsten-thorium wire, or of a tungsten of molybdenum wire coated with a barium-strontium emission paste, is wound continuously on the U-shaped molybdenum caps 2 and 3. During winding, the parts of the wire 1 which are to engage the caps 2 and 3, are made bare of emissive material by means of a scrapper (not shown), at least in those places which come into contact with the caps.

The caps 2 and 3 are supported in a slidable manner by the supporting plate 4 which in this case consists of ceramic material. Between the caps 2 and 3, respectively, and the supporting plate 4, the supporting rods 5 and 6, respectively, are provided and welded to the caps. Supporting wire 5 is afterwards mounted in the electrode system on a supporting rod while the supporting wire 6 is provided with a brace 7.

The cathode forms a unit which can be easily handled. After mounting in the electrode system, a cross brace 15 is provided on the brace 7 which is pulled downwards by springs 8 and consequently strains the wire 1 in that the caps 2 and 3 are slideable on the supporting plate 4.

In order to reduce the cost of manufacture of the cathode, the ceramic plate 4 in the embodiment shown in FIGS. 3 and 4 is replaced by a mica plate 11. Such a mica plate is in addition less breakable than a ceramic plate. Since a mica plate is comparatively flexible, the caps 2 and 3 are welded on metal cylinders 9 and 10 having a rectangular cross section, which support the mica plate 11 through the greater part of its length and can slide on it. In this embodiment, the tungsten cathode wire 1 which has a thickness of 27 microns and is coated with an emitting layer of 20 microns in thickness, is wound 20 times on the caps 2 and 3 so that the cathode consists entirely of 40 wire parts having a total surface area of 2 cm. The total length of the cathode unit without the braces 5 and 6 is 38 mm.; the width of the caps 2 and 3 is 5 mm.; the wound width is 4 mm. The wall thickness of the caps 2 and 3 is 0.25 mm., and that of the cylinders 9 and 10 is microns, and the thickness of the mica supporting plate is 0.4 mm. The total thick ness of the cathode unit is 1.3 mm. The current strength is 3 amp. at a filament voltage of 1.4 to 1.6 volts.

In the embodiment shown in FIG. 5, a supporting plate 12 consisting of metal, for example molybdenum, is used which is coated at the ends with insulating layers 13 and 14 so as to avoid a short-circuit of the caps 2 and 3. This plate 12 may be coated with zirconium powder and then also operates as an ion trap if a relatively small negative voltage, i.e. 10 to 50 volts, is applied to it.

The cathode according to the invention very rapidly reaches the operating temperature owing to the use of thin wires and is highly suitable for transmitting tubes for very short waves, since the thin wires situated close to one another, emit as a surface, while the two cathode surfaces are separated by the supporting plate, so that a definite transit time is obtained. Since the electrons can travel from one cathode half to the associated half of the system only, all the electrons cover an equal distance. In addition, the inductance of the supply conductors and the cathode wires is small.

Will'be readily apparentto those skilled in this art with out departing from the spirit and scope of our invention which is defined in theappended claims.

What we claim is: 1. A directly heated cathode foran electric discharge tube comprising a support, a pair of U-shaped metal :caps insulated from one another slideably mounted on opposite ends of said support, and a plurality of paral- ;lel-connected thin Wires woundonsaid U-shaped metal caps. 7 a

2. A directly heated cathode unit asclaimed in claim 1, in which the supporting plate is constituted of ceramic --material.

3. A cathode unit as claimed in claim 1, in which the '4. A cathodeunit as claimed .in claim '1', in which the supporting plate is metal coated at two oppositely located ends with insulating material, on which ends the U-shaped caps are slidably mounted and attached;

5. A cathode unit as claimed in claim 4, in which the supporting piate is coated with zirconium. whereby'with a negative'potential with respect to the cathode applied thereto, it operates as an ion'trap. Z

6. A cathode for an electric discharge tube comprising a support, U-shaped metal caps insulated from one another and slideably mounted on said support, aplurality of parallel-connected thin wires wound on said metal caps, and resilient means engaging said caps for imparting tension to said wires mounted thereon.

References Cited by theExaminer UNITEDSTATES PATENTS 1,273,630 7/18 Langmuir a 313-343 X DAVID ,J. GALVIN, Primary Examiner.

RALPH G. NILSON,ARTHUR1GAUSS, Examiners. 

1. A DIRECTLY HEATED CATHODE FOR AN ELECTRIC DISCHARGE TUBE COMPRISING A SUPPORT, A PAIR OF U-SHAPED METAL CAPS INSULATED FROM ONE ANOTHER SLIDEABLY MOUNTED ON OPPOSITE ENDS OF SAID SUPPORT, AND A PLURALITY OF PARALLEL-CONNECTED THIN WIRES WOUND ON SAID U-SHAPED METAL CAPS. 